The Brent Spence Bridge and other Ohio River spans remain under the watchful eye of law enforcement.

The bridges are also on a constant checklist by the U.S. Coast Guard.

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"We know what's going on down there," said Lt. Rob Reinhart, of the Coast Guard. "I'm not saying people couldn't sneak things in, but we have a pretty good network."

Five men associated with the Occupy Cleveland group were arrested Tuesday in connection with a plot to blow up a northeast Ohio bridge.

The FBI said the suspects bought the explosives  actually fake  from an undercover employee and put them at the base of a highway bridge over the Cuyahoga Valley National Park, about 15 miles south of downtown Cleveland, on Monday.

After leaving the park, they tried to initiate the explosives using a text-message detonation code, and they called the person who provided the bombs to check the code when it failed, according to the FBI affidavit.

The incident spotlights the vulnerability of the Tri-state's many bridges.

"We recognize the impact those bridges have to commerce, and so that's something we're always concerned and we're always watching," said Chief James Craig, of Cincinnati police.

"While what happened up in Cleveland can happen anywhere in the U.S., downtown Cincinnati has a lot of bridges, and we rely on them, especially as we talk about infrastructure," Reinhart said. "We're here to protect our little piece of the pie."

Authorities also said an important piece of their safety net is the public's awareness.

"What may appear to be something small could be something major," Craig said.